JustKernel

Ray Of Hope

October, 2016

basic programs to clear the concepts

Userspace and kernel space virtual address space division. TO understand the address space allocation between user space and kernel space I wrote this simple program. Kernel space: 10 int init_module(void) 11 { 12 void * kern_mem; 13 kern_mem = kmalloc(5, GFP_KERNEL); 14 printk(KERN_INFO “Hello world addr=%lx”, (unsigned long)kern_mem); 15 return 0; 16 } O/P : […]

Posted in Basic C | 1 Comment »

braindump- memory corruption

Linux kernel 3.10 has somewhat dubious use of __GFP_WAIT which is more recent kernel has been replaced __GFP_RECLAIM and __GFP_DIRECT_RECLAIM which are more sensible . I have been debugging a customer issue where AMD GPU passhtrough for S9050 card is causing XenServer host running 3.10 kernel to crash but XenServer 7.x Tech Preview release with […]

Posted in debugging, Linux Kernel, Xen, Xen | No Comments »

XSM-Flask / Xen Credit-2 scheduler

Below are the links for my talk at XenSummit 2016 Toronto on 1) XSM/Flask current architecture, its shortcomings and new approach. 2) Credit-2 scheduler benchmarks and comparative results with Credit-1. Xen Credit-2 Scheduler Performance Benchmarks XSM Flask Let me know in case of any queries. Anshul Makkar anshul_makkar@justkernel.com

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brain-dump: ballooning bug.

For past 3-4 days I have been working on a problem where after a series of ballooning operation involving in the range of 512 MiB to 30 GiB , the guest (Ubunut 16.04 ) crashes. Logs were: [ 193.432063] Freezing remaining freezable tasks … [ 198.032804] ata2.01: qc timeout (cmd 0xa1) [ 198.032815] ata2.01: failed […]

Posted in Uncategorized | No Comments »